1. FIELD OF THE INVENTION
This invention relates generally to the field of carbon fibers, and relates specifically to the field of enhancing combustion of carbon fibers.
2. PRIOR ART
The increasing use of carbon fiber-reinforced-resin matrix composites in aircraft construction and in sporting goods raises the prospect of potentially serious problems when these materials are involved in accidents accompanied by fire or are disposed of by incineration. When the binding resin matrix in such composites is destroyed by combustion, the fibers resist incineration and their light weights and high aspect ratios combine to facilitate their being lofted in an air current. Frequently the lofted fibers settle on electrical equipment where their high electrical conductivity may cause shorting and consequent failure of the equipment. This phenomenon is well known in the carbon fiber manufacturing community where extreme measures are needed to protect against fiber escape and attendant equipment malfunction.
The problems posed are potentially serious and they will assuredly be aggravated as expected usage of carbon-resin composites materializes in automobile manufacture, prompted by a reduced weight approach to achieving government-mandated environmental and energy goals.
Possible solutions to the problem abound, but so far none has been satisfactorially demonstrated. Among the possible solutions are: Modifications in fiber processing to reduce electrical conductivity, the practical limit to this approach is not known, but the value of electrical resistance already achieved is 10.sup.5 to 10.sup.6 ohm/cm and this is not adequate in many situations. Use of exotic resin matrices to insure a high yield of stable char which would retain carbon fiber, preventing its escape, but the exotic resins tend to be expensive and difficult to process so that their use may be resisted by manufacturers. Coating carbon fibers with high electrical resistance materials, generally these coatings are brittle, adhere poorly to carbon, and would require several years to satisfactory development; and exclusive disposal in sanitary landfill, this does not provide a solution for the accidental fire problem, cannot be controlled since the uninformed may still dispose for routine incineration, and in any case only defers the problem to a later time. The above problems are discussed in detail in a NASA Technical memorandum No. 78761 by Dennis L. Drew, dated July, 1978.